Multiplex telegraphic and telephonic system



Sept. 21, 1937.

W. A. LOTH ET AL MULTIPLEX TELEGRAPHIG AND TELEPHONIC SYSTEM Filed Jan. 17, 1936 igf 2 Sheets-Sheet 1 Sept. 21, 3937. w. A. LOTH ET AL 2,093,812

MULTIPLEX TELEGRAPHIC AND TELEPHONIC SYSTEM 7 Filed Jan. 17, 1936 2 Sheets-Sheet 2 Patented Sept. 21, 1937 t UNITED STATESv ATENT OFFICE MULTIPLEX TELEGRAPHIG AND TELE- PHONIC SYSTEM William Arthur Loth and Joseph Armand Givelet, Paris, France Application January 17, 1936, Serial No. 59,484 In France January 19, 1935 9 Claims. (Cl. 179-4) In order to double the number of telephonic formers (in the known manner) of a very ecoor telegraphic messages or communications, on nomical construction. In fact, it is known that one single circuit, use is made of the persistency the output will be maximum when the impedance of the sound impressions on the ear, the two of the transformer winding is equal to the inside simultaneous transmissions being alternately resistance of the rectifier. This latter resistance broken and riding on each other, and the frebeing low, the transformer may also have a low quency of the interruptions being sufiiciently impedance, which has still a favourable influence high to allow each auditor on the receiving side on the fading of the connections. to have the impression of continuous reception. Finally, the solid contact rectifiers being gen- 1 For this purpose, both the transmitter and the erally conceived as a pile of washers, intermel0 receiver sets are provided with valves, placed in diary taps may be arranged and the middle point opposition and comprising a neutral point, the may be displaced to the neutral point of the sysline being energized or fed by a current of nontem in order to obtain the best possible equilibaudible frequency. rium, which is very important for eliminating the This system, though eloquent in theory, meets diaphony and the riding or overlapping of the 15 with serious difficulties in the practical realizalimits of intercutting of the conversations, this tion. In fact, the valves with hot filament have being impossible with the lamp valves.

a resistance of at least 1000 to 1200 ohms, for it In order to prevent the return of the teleis not possible to realize cathodes of a big size phonic currents to the oscillator for dividing or emitting electronic torrents, the heating current intercutting, it is advantageous, according tothe 0 expense becoming a prohibitory one. On the invention, to make use of anti-resonance cirother hand, the valves with a gas filling (argon, cuits tuned on an average speech frequency, 800 neon, vapour of mercury or the like) are not able cycles for example. These circuits Offer a great to be used in telephony on account of the audible resistance to the passage of the currents of midisturbances caused by the transformation of the crophonic origin, having an audible frequency 25 molecules of the gas filling, by the setting in of and allowing, Oh the Contrary, the higher arcs or the like. quencies to pass easily. Adjustable supple- It may also be noted that concerning the telee y resistances y be provided to Complete phonic connections between two different cities, the adjustment of the neutral points.

the public services of the different countries ad- According to the invention, the anti-resonance 30 mit only a fading tendency generally below 1,3 circuits may also be replaced by low capacities napier. Consequently, the hot cathode or gas (of about 1/1000 microfarad) opposing a. strong filling valves are not appropriate, and the object impedance to the audible frequencies and a slight of the present invention is to replace these valves impedance to the higher frequencies. It is also only by rectifiers with a solid contact of low ohmic possible to utilize any other filtering system, as 35 resistance, such as cuproxide, seleno-iron, zincknown in electrical engineering. ite-chalcopyrite or similar contacts. For calling up the receivers invited to enter a The installation is very much simplified by conversation, the present invention provides a eliminating the heating current and utilizing only call finder or annunciating device on each branch the current for feeding a high frequency local with rectifiers placed in the suitable direction and 40 oscillator adapted to interrupt the message at a an excitation by direct current or alternating frequency imperceptible to the ear, so that the current. message seems continuous. One such oscillator In the case of direct current, this current is is used for every two stations. supplied to the line with a suitable polarity for The solid contact rectifiers may have an ohmic releasing the Call finders annunciating 45 resistance for the suitable current direction of mentsof the receivers to be called up. This ouronly 100 t 200 ohms, a d th ystem15 c idrent does not disturb the conversations, and it erably more efiicient with respect to that utilizing COIItIOIS an p l signal W passing in the filament or rarified gas valves. It is then possiwanted direction, controlled by the rectifiers.

ble to observe the prescribed limits of admitted In the case of alternating current, an inverter 50 fading, which was practically impossible with the has to interfere. The call is effected between a filament valves. Wire and the ground connection on both the Another advantage of the solid contact rectilines, the alternating cu ent source havin One fiers, owing to their low resistance, is the possipole grounded. It is thus possible to call up the 55 bility of associating these rectifiers with transwanted station owing to suitable indications for the correct manipulation of the inverter at one and the other station.

The accompanying drawings, given solely by way of example, show two diagrams of connection according to the invention.

Fig. 1 is a diagram of connection of stations provided with call finders, excited by direct current.

Fig. 2 shows a diagram of connection of sta tions provided with inverters for calling up by alternating current.

As will be seen in Fig. 1, an oscillator I supplies the wires 2 and 3 of the line with high frequency currents for obtaining the intercutting of the conversations. Between the oscillator I and the wires of the line, anti-resonance devices 4 and 5 are interposed and tuned on about 800 cycles, average frequency of the conversations. Adjustable resistances 6 and I ensure the equilibrium of the connections of the oscillator with the wires 2 and 3.

The subscribers are connected to the system by means of plugs, penetrating into jacks 8, 9 at one station and 8', 9 at the other one. These jacks are connected to primary windings Illa of responsive transformers I9 and I I, I0, and II. The secondary windings lb of these transformers are mounted between the wires 2 and 3, and shunted by a capacity respectively I2, I3, I2, I3, which allow the high frequency intercutting circuits to pass through, but prevent the passage of low frequency currents.

Rectifiers I4 and I4, arranged in the same direction, connect the secondary windings to the wire 2. Thus, the jacks 8, 8 may be interconnected, for the current flows in the same direction through I4 and I4.

Small regulating resistances I5, I5 associated with I6, I6 permit the equilibration of the two branches from a neutral point I'I, I1. 0n the side extending from I1 or IT to the wire 3, a call finder or annunciating element I8 or I8 is arranged in combination with rectifiers I9 or I9 respectively of'the same direction as I4 or I4.

As to the other stations 9, 9 which are interconnected, there is the same rectifying arrangement 20 and 20 of the same direction (opposite to that of I4 and I4) with small regulating resistances 2|, 2|, 22, 22 on both the ends and neutral points 23 and 23'.

The regulating resistances on the ends are provided so as to have the same voltage exactly in the neutral points I! and 23 on one side, and I1 and 23 on the other side so that it may be possible to join the neutral points with a common neutral point 24 or 24 (which is shown in dotted lines on the drawings) which may be connected to the ground, thus facilitating the grounding of all the frames of elements, transformers for example,

In order to release the annunciating elements, the wires 2 and 3 of the line are supplied with a direct current of the suitable direction for actuating the annunciating elements corresponding to those of the jacks which are to be connected to two subscribers sets destined to communicate with each other, such as for example 8 and 8. The annunciating members I8 and I8 are then released simultaneously, the current flows through the two corresponding branches, but it cannot pass to the two other branches and thus, the conversations between 9 and 9' are not disturbed when the jacks are occupied by the subscribers plugs.

The operator of the central station sees immediately which of the jacks is free and which is the direction of the current to be supplied for exciting the corresponding annunciating members. It is easy to provide the switchboard with clear indications so as to avoid errors.

On Fig. 2, there are arrangements of the same kind, nevertheless the jacks have been arranged at each station on opposite rather than semibranches, which does not modify at all the working, but permits having one call for each alternating current source 25. The two neutral points I! and 23 on one hand, and I1 and 23 on the other hand have a common grounding contact 26 and 26. The alternating current sources 25, 25' of each station have one of their wires connected to the ground; wire 2! and 21 respectively. The other wire comprises an inverter 28, 28 which may be connected to contacts 29, 30, and 29, 30'.

Suppose the key, as shown in Fig. 2, at the first station is in contact with the plug 29, the alternating current will fiow in wire 2 and return to the earth 26, exciting the annunciating member 3|. At another station, equally, the current will flow through the annunciating member 3| and continue to the earth 26. The same phenomenon will be produced and the same annunciating members will be released, when at the second station the key is in contact with the plug 29. In the case of one or the other of the keys being in contact either with the plug 30 or with the plug 30, it is obvious that the other annunciating members 32 and 32 would be excited.

Of course, the subscribers jacks will be arranged according to the known practice in telephony:

For example, these jacks may be provided with supplementary contacts short-circuiting the corresponding annunciating member during the conversation as soon as the plug is inserted. The elimination of the annunciating member from the circuit increases namely the efficiency of the plant.

Finally, in spite of all precautions taken in order to prevent a disequilibrium, it is still possible that same may somewhat interfere, but in this case, only a slight diaphony would occur during two simultaneous conversations.

However, practice has shown that it is quite possible to suppressthe insignificant diaphony which may exist, with the aid of the means which constitute the object of the present invention.

These means are based upon the following considerations:

The currents which produce the diaphony, are always very weak with respect to those of the normal conversations. The voltages corresponding to the diapho'nic currents are equally very weak with respect to the voltages which correspond to the normal telephonic currents.

For suppressing the diaphonic currents without affecting the normal currents, use is made of conductors or conductor elements which are not affected by the ohmic principle and whose re sistance increases considerably when the voltage rections so as to allow both the alternations to pass continuously withoutaltering the voice.

All of these elements are preferably inserted on each subscriber's line or on the winding of the transformer corresponding to this line.

We claim:

- 1. Multiplex telegraphic and telephonic system for simultaneously carrying two messages on a single circuit, comprising in a circuit a source of current of non-audible frequency for interrupting the normal message-carrying current in said circuit, branches across said circuit, solid contact rectifiers of weak ohmic resistance, placed in opposition insaid branches, having a neutral point from which the apparatus on both sides thereof may be balanced potentially, a group of said rectifiers being provided on each side of the neutral point of each branch; variable resistances for putting the neutral points in the same electric condition; anti-resonance devices tuned on an average speech frequency connected to each branch between said branches and said source; and small resistances arranged in series with said anti-resonance devices.

2. Multiplex telegraphic and telephonic system for simultaneously carrying two messages on a single circuit, comprising in a circuit a source of current of non-audible frequency for interrupting the normal message-carrying current in said circuit, branches across said circuit, solid contact rectifiers of weak ohmic resistance, placed in opposition in said branches, having a neutral point from which the apparatus on both sides thereof may be balanced potentially, a group of said rectifiers being provided on each side of the neutral point of each branch; variable resistances for putting the neutral points in the same electric conditions; anti-resonance capacities tuned on an average speech frequency connected to each branch between said branches and said source; and small resistances arranged in series with said capacities.

3. Multiplex telegraphic and telephonic system for simultaneously carrying two messages on a single circuit, comprising in a circuit a source of current of non-audible frequency for interrupting the normal message-carrying current in said circuit, branches across said circuit, solid contact rectifiers of weak ohmic resistance, placed in opposition in said branches, having a neutral point from which the apparatus on both sides thereof may be balanced potentially, a group of said rectifiers being provided on each side of the neutral point of each branch; variable resistances for putting the neutral points in the same electric condition; anti-resonance devices tuned on an average speech frequency connected to each branch between said branches and said source; small resistances arranged in series with said anti-resonance devices; an annunciating member or call finder on each branch and having a winding, and a capacity shunted on the winding of each annunciating member.

4. Multiplex telegraphic and telephonic system for simultaneously carrying two messages on a single circuit, comprising in a circuit a source of current of non-audible frequency for interrupting the normal message-carrying current in said circuit, branches across said circuit, solid contact rectifiers of weak ohmic resistance, placed in opposition in said branches, having a neutral point from which the apparatus on both sides thereof may be balanced potentially, a group of said rectifiers being provided on each side of the neutral point of each branch; variable resistances for putting the neutral'points in the same electric condition; anti-resonance devices tuned on an average speech frequency connected to each branch between said branches and said source; small resistances arranged in series with said anti-resonance devices, a jack and an annunciating member on each branch and constituting a station, said solid contact rectifiers being disposed in opposite directions at each of the stations respectively.

5. Multiplex telegraphic and telephonic system for simultaneously'carrying two messages on a single circuit, comprising in a circuit a source of current ofnon-audible frequency for interrupting the normal message-carrying current in said circuit, branches across said circuit, solid contact rectifiers of weak ohmic resistance, placed in opposition in said branches, having a neutral point from which the apparatus on both sides thereof may be balanced potentially, a group of said rectifiers being provided on each side of the neutral point of each branch; variable resistances for putting the neutral points in the same electric condition; anti-resonance devices tuned on an average speech frequency connected to each branch between said branches and said source; small resistances arranged in series with said anti-resonance devices; a source of direct current for supplying the call up current, means for sending this current in the suitable direction depending on the annunciating member to be released and the direction of the rectifiers to be crossed.

6. Multiplex telegraphic and telephonic system for simultaneously carrying two messages on a single circuit, comprising in a circuit a source of current of non-audible frequency for interrupting the normal message-carrying current in said circuit, branches across said circuit, solid contact rectifiers of weak ohmic resistance, placed in opposition in said branches, having a neutral point from which the apparatus on both sides thereof may be balanced potentially, a group of said rectifiers being provided on each side of the neutral point of each branch; variable resistances for putting the neutral points in the same electric condition; anti-resonance devices tuned on an average speech frequency connected to each branch between said branches and said source; small resistances arranged in series with said anti-resonance devices; a ground contact connected to the neutral point on each branch, a receiving station provided at each branch, a source of alternating current at certain of the stations, a reversing change-over switch on each of the stations, connections for sending the alternating current for calling up in the wanted direction, and a. ground connection for one of the poles of the alternating current source.

7. Multiplex telegraphic and telephonic system for simultaneously carrying two messages on a single circuit, comprising in a circuit a source of current of non-audible frequency for interrupting the normal message-carrying current in said circuit, branches across said circuit, solid contact rectifiers of weak ohmic resistance, placed in opposition in said branches, having a neutral point from which the apparatus on both sides thereof may be balanced potentially, a group of said rectifiers being provided on each side of the neutral point of each branch; variable resistances for putting the neutral points in the same electric condition; anti-resonance devices tuned on an average speech frequency connected to each branch between said branches and said source; small resistances arranged in series with said anti-resonance devices; a jackand an annunciator mounted in each branch; a bladeon each jack, and connections to said blades for switching off the annunciators. v

8. Multiplex telegraphic and telephonic system for simultaneously carrying two messages on a single .circuit, comprising in avcircuit a source of current of non-audible frequency for interrupting the normal message-carrying current in said circuit, branches across said circuit, solid contact rectifiers of weak ohmic resistance, placed in opposition in said branches, having a neutral point from which the apparatus on both sides thereof may be balanced potentially, a group-of said rectifiers being provided on each sideof the neutral point of each branch; variable resistances for putting the neutral pointsin'the same electric condition; anti-resonance devices tuned on an average speech frequency connected to each branch between said branches and said source; small resistances arranged in series with said antiresonance devices, subscribers lines leading from said branches, and a unit of two elements of imperfect contact mounted in inverse directions and branched in parallel on each subscribers line.

a 9.. Multiplex telegraphicand telephonic system for simultaneously carrying two messages on a single circuit, comprising in a circuit a source of current of non-audible frequency for interrupting the normal message-carrying current in said circuit, branches across said circuit, solid contact rectifiers of weak ohmic resistance, placed in opposition in said branches, having a neutral point from which the apparatus on both sides thereof may be balanced potentially, a. group of said rectifiers being provided on each side of the neutral point of each branch; variable resistances for putting the neutral points in the same electric condition; anti-resonance devices tuned on an average speech frequency connected to each branch between said branches and said source; small resistances arranged in series with said antiresonance devices, transformers having their pri- .mary windings connected respectively in said branches, and subscribers lines leading respectively from the secondary windings of said transformers.

WILLIAM ARTHUR LO'I'H. JOSEPH ARMAND GIVELE'I. 

